Primitive Archer
Main Discussion Area => Bows => Topic started by: TreyNC on January 07, 2009, 10:08:14 pm
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The bow is still in tillering, it's a one piece white oak board bow. Raw hide backed, 68", 2" wide at fades in a pyrimid style to .5" at tips. Here is the situation, Limb A is thinner (slightly) than limb B, limb A is also stiffer than limb B. No obvious flat spots or hinges in either limb so far. When pulled on the tillering board to current position limb B pulls about .5" further than limb A. I am just a little nervous about removing wood from the thinner limb. Maybe a little gun shy! I have been very careful not to pass the intended draw weight. I will have to remove more wood from both limbs for sure to reach what I want. Who thinks what?
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use the stiffer limb as the lower limb.
you want that to be a little stiffer any how,half inch is good for that.
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I'd do like Tim said. Wood is funny, sometimes it can vary in density from one end of a board to the other. The bend is the main thing, trust the bending more than the measurements.
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Like above said,I trust the bend and after I start tillering I don't pay much attention to the
measurements. Like also said make the stiff limb the bottom. :)
Pappy
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With a pyramid bow there is little to no thickness taper as the taper is along the length of the limb. So I would consider side tillering
and its possible that the limbs are not truly the same width and taper and the stiff limb has more width and hence is stiffer.
Depending on the draw weight and length your going for 2" wide at the fades may be overkill, look into badgers mass theory
it is a useful tool. Also you didn't mention how far along the tillering is, is it braced yet? and if so how far have you tillered it too?
One more thing closely monitor the set each limb is taking and where in the limb its being taken, this can provide an important clue as
to what is really taking place. Good Luck eh :)
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As some of the other guys mentioned, could be a difference in density. Very common in staves. This will certainly cause different limb dimensions. Could be a moisture problem too. Could be an uneven limb stress problem also. Going to need a little more info from you for us to sort it out.
Was your board stored vertically on horizonally prior to starting your bow? That could cause uneven moisture content from limb to limb. Is your bow a symmetric or asymmetrical design? Intended arrow pass measurement from center? Are you pulling the bow using a tillering tree? If using a tillering tree are you pulling from dead center or slightly off center?
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Let me back up a minute here. First thing you should check for is equal limb mass. You do this by marking your bow dead center and balancing on a pencil or like and see where it balances in relation to your center mark. -ART B
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Thanks for the replies. Here is some more info.
Symmetrical design. Arrow pass above center. I was careful about width taper, not that I believe it's perfect. I will mass test it when I get home. It is braced at four inches and have pulled the tips back another three inches. Moisture when started not a problem I checked with a meeter, since started has been kept in a dry place. Ass far as width, I have been having some issues with string follow. Also this bow is for a coworker with gorilla arms. He pulls 29 1/2". I am trying to get around mid to low 50's. On the subject of string follow, after unbracing one limb is 1 1/8" and the other is 1 3/16" and I will have to check which is which when I get home. The stave started with one limb with 1/2" set and the other 3/8" set from the get go. Don't know which one was which though.
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I would get it out to at least 24" and then heat in some reflex and toast the belly. With a 30" draw
you better get every inch of limb bending that you can.
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With TB II already on it is it possible to heat it enough to reflex it?
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With it already backed with rawhide, it could cause a problem putting heat to it I would think. Maybe someone else has attempted that and can respond. If I did try to heat and reflex it, I think I'd try and protect the back/rawhide as much as possible, maybe tape aluminum foil along the edges or something similar.
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Sorry about that I forgot that said it was backed, don't try to heat it with a backing the glue would release.
I guess you could remove the backing and reapply it after adding reflex and tempering the belly.
Are yuou sure your friend has a 30" draw, if thats his draw length on a compound its most likely quite a bit shorter
on a real bow. I've seen some big guys and they only pull 28"
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No that's correct, I measure mine at 27 1/2" and his is 2" longer than mine to corner of mouth.
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Arrow pass how far above center?
Glad you guys brought up the rawhide back. Trey, the weight (or difference in weight of the rawhide backing from limb to limb) of the rawhide may make it impossible to get an accurate reading on the balancing of the limb's mass weight. But you still want to go ahead and do that. Maintain your center mark/balancing act throughout the tillering process to the finished bow. Mass is mass be it wood or rawhide or as in your case both.
If you're careful you can get away with heating your bow with the rawhide backing. I've done several like that. Most of your set is probably from fades to mid-limb or the widest part of your limbs. Keep your heat gun very close to the wood and don't let the heat radiate over the edges if possible. Keep a close check on the back as you procede. As your limbs warm up just start reflexing backwards to where you want and finish your heating. Let cool in place and wait several days for re-hydration. Don't try for a deep dark toasting job as this may penetrate to the back and effect the backing. Since you're going to remore most of the heat treating (here some side tillering is desirable if width permits to maintain some of your heat treating) during your final tillering you'll want to repeat the process again right before you reach desired draw. -ART B
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Trey, good for you for noticing. What I do is begin to narrow the stave when I think it's getting to thin. The wood is trying to tell you something. You gotta listen, figuratively. :) Jawge
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I learned that lesson the hard way years ago when I thinned a naturally reflexed area on the lower limb a bit too much tryiung to get it ti respond to wood removal. My punishment was a thump on the head when the limb broke. :) Jawge
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That's funny Jawge (you know now not then). Well I did check mass and looks like the stiffer side is heaver. I then made one inch marks on both limbs from tips up, using OD caliper discovered the stiffer limb is wider! I couldn't tell it with just a tape measure, but it is. Didn't get a chance to mess with it tonight I needed to play with my son some before mommy got home. I will get on it tomorrow and work the sides.
Thank you to every one who joined in on this one!
Now if I can get the rest of the bow to come out right, I have never made one to pull this far before.
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ohh yeah
thats one of my favorite tools when setting up the profile and all thru floor tiller and long string tiller
i use a digital one.
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I had a feeling that one side was a bit wider Trey, on a pyramid bow once both limbs are bending the same I like to side tiller
to bring in the final weight. Can't wait to see it done :)